I regularly write scripts that involve more than one virtualenv. At the moment this is trivial by just activating and deactivating envs from one script. Starting subshells is complicated because communication into the shell barely exists. Worse than that is that the shebang only supports two arguments and is heavily length limited.
Unless you are rapidly switching envs, you could launch the parts of your scripts that operate on different envs as subscripts. Then you can pipe data in and out. Can you provide an example where this does not work?
